This invention relates to ball point pens.
Various types of ball point pens are in widespread use, for example, those in which the entire pen is disposable after the ink supply has been used, and "retractable" ball point pens in which a ball point refill is spring-loaded within a permanent outer body. The term "ball point pen", as used herein, refers to both disposable pens and ball point refills.
Ball point pens generally include a tubular member in communication with an ink supply, a socket formed at the tip of the tubular member which receives a spherical ball and terminates in deformable rim structure dimensioned to retain the ball, ball seat structure at the base of the socket against which the ball is seated, and an ink feed system extending from the ball seat to the ink supply for supplying ink to the surface of the ball. The ink feed system is typically arranged so as to provide a uniform flow of ink to the ball, e.g., in a star shaped arrangement of capillary channels which radiate out from a central aperture in communication with the ink supply. In some cases, wear of the ball seat during extended use of the pen may cause the channels of the aperture to become blocked by the ball
The ink flow, or "ink laydown" i.e., amount of ink which is deposited for a line of a given length, from the ball point has traditionally been controlled by precisely controlling the socket diameter. The socket is initially bored to a diameter which has approximately the same diameter as the ball (typically up to one percent larger for a brass socket, and up to one percent smaller for a stainless steel socket), capillary flow passages are formed in the base of the socket by a metal punch operation, the ball is inserted into the socket and hammered to form a conforming ball seat at the base of the socket, and then the ball is freed by spinning the outer surface of the rim structure to stretch and deform the wall of the socket slightly away from the ball. If the desired ink laydown is not obtained using a given initial socket diameter, different initial socket diameters are tried until a desired laydown is obtained. To vary the diameter of the socket, it is necessary to adjust the boring tool, and carefully measure the resulting diameter using specialized equipment, a labor-intensive procedure requiring a highly skilled worker. Each time a new lot of point metal is used in the manufacturing process, this labor-intensive set-up procedure must be repeated.